The field of the present invention generally relates to optical systems for data reading and radio frequency identification (RFID) systems for remote identification of physical objects. More particularly, the field of the present invention relates to methods and apparatus for enabling a data reader with an electronic article surveillance (EAS) antenna to read RFID data.
Optical reading systems are widely used to read data in the form of bar codes or other encoded symbols printed on various objects. These systems may be used in a wide variety of applications, such as inventory control and point-of-sale transactions in retail stores.
Optical reading systems may employ an optical reader that illuminates a bar code and detects light reflected from the bars and spaces of the code, although such systems may be configured to operate in ambient light conditions. In one type of optical reading system, an optical beam of light produced by a laser diode is used to scan the bar code symbol. The bars of the code absorb light, while the spaces of the code reflect light. The resulting pattern of reflected light is detected by circuitry within the optical reader. The reflected light can be detected by a sensor such as a photocell, photodiode, CCD array, or CMOS array sensor.
After the bar code data is received by the optical reader, the sensor signal may be subject to filtering, amplification, digitization and decoding. The detected signal may be transmitted to a processor or decoder located within the optical reader, or to a separate device such as a personal computer. In systems where the signal is conveyed to a separate device, the optical reader may be connected to the external data processor by means of cables or via a wireless communication link. The wireless communication link can be implemented using radio frequency (RF) equipment or infrared (IR) transmitters and receivers, for example.
In retail stores, stationary optical reading systems may be set up at check-out stands and may be built into a horizontal check-out counter, so that items to be purchased can be placed on a counter, deck or conveyor, and then moved through an optical reading area. An example of a stationary optical reading system is described in U.S. Pat. No. 5,837,988, hereby incorporated by reference as if set forth fully herein. Alternatively, the optical reader may be a handheld device, in the shape of a wand or gun. An example of a handheld data reader is described in U.S. Pat. No. 5,475,206, hereby incorporated by reference as if set forth fully herein. Typically, in operation these handheld devices are pointed or aimed at the retail item, so that a wide range of information, including price, may be read from the object.
Some optical readers are equipped with EAS antennas, enabling them to be used with EAS systems. EAS systems are typically used to prevent theft, by detecting tags or hidden labels located on any unpurchased items, as they pass through the exit of a retail store. In a common system, a transmitter sends a radio frequency (RF) signal to a tag, and the tag sends back a response signal, which is detected by a receiver. In some systems, the transmitter and receiver may be combined into one single antenna.
If a tag is detected by the EAS system, an alarm will be triggered indicating that a item that has not yet been purchased, is being taken from the premises. To prevent the alarm from being triggered by a purchased item, the tag must be removed or deactivated at time of purchase. In some systems the tag must be physically removed from the item, while in others, the tag may be disabled electronically. Once the tag is removed or disabled, the purchased item will no longer be detectable by the EAS system. Thus, in a common EAS system a retail item is either detected or not detected.
RFID systems can be used to identify retail items by reading information stored on tags or hidden labels on the items. Such systems do not merely detect the presence or non-presence of a tag. Instead, these systems can be used to remotely identify physical objects by the response signal sent back by the tag.
An RFID system typically employs at least two components, a xe2x80x9ctransponderxe2x80x9d or xe2x80x9ctag,xe2x80x9d which is attached to the physical item to be identified, and a xe2x80x9creader,xe2x80x9d which sends an electromagnetic signal to the transponder and then detects a response. Typically, the reader emits a RF signal, which is received by the transponder, after the transponder comes within an appropriate range. In response, the transponder then sends its information via a modulated RF signal back to the reader. The reader detects this modulated signal, and can identify the transponder by decoding the modulated signal. After identifying the transponder, the reader can either store the decoded information or transmit the decoded signal to a computer.
In a conventional RFID system the transponder may be either xe2x80x9cpassivexe2x80x9d or xe2x80x9cactive.xe2x80x9d A passive transponder is usually a simple resonant circuit, consisting of an inductive coil and a capacitor. Passive transponders are generally powered by the carrier signal transmitted from the reader. Active transponders, on the other hand, require their own battery source.
An optical reader equipped with EAS antennas will not work with RFID reading systems. EAS systems typically operate at frequencies in the range of 8 to 9 MHz. However, typical operating frequencies for RFID systems are 13.56 MHz, 915 MHz and 2450 MHz. Thus, attempting to connect an optical reader equipped with an EASA antenna would lead to unacceptable distortion of the signal, including signal reflection and possible loss of data. The inventor has therefore recognized that it would be advantageous to provide a mechanism and method for allowing an RFID reader to operate with an optical reader equipped with an EAS antenna.
The present invention relates to methods and apparatus for enabling a data reader with an EAS antenna to read RFID data. In one embodiment, a dual ended cable connects an EAS antenna located on a data reader with a separate RFID reading device. The dual ended cable, has different termination impedances at either end, and includes an impedance matching network on one end. The dual ended cable preferably has a characteristic impedance of a standard value, such as 50 ohms or 75 ohms, throughout the dual ended cable, except at the end having the impedance matching network. In an exemplary embodiment, the impedance matching network has a characteristic impedance equal to that of an EAS antenna located on a data reader. The end of the dual ended cable having the impedance matching network may be connected to the EAS antenna on the data reader, and the coaxial cable may be connected to a RFID reader, thereby minimizing distortion in the signal transmission and maximizing the power transfer between the data reader and the RFID reader.